IB Environmental Systems and Societies/Changes
2.6.1 Limiting factors constrain populations from continuing to grow for ever Density dependent factors: operate as negative feedback mechanisms, regulating the population and leading to stability. E.g. competition for resources, disease, predation, size of territory Density independent factors: Generally abiotic. E.g. weather, long-term climate change, tsunamis Carrying capacity is the maximum number of organisms which are able to live in an area
2.6.2 J-curve: has no limiting factors, only shows exponential growth and doesn’t slow down. S-curve: has 4 different stages: the lag phase, the exponential phase, the transitional phase and the stational phase. Slows down as carrying capacity is reached.
2.6.4 Life strategies r-strategy: mostly goes for small animals which produce large amounts of offspring, most offspring dies early and individuals who survive are very likely to live for a long time. Curve: J-curve K-strategy: almost all individuals survive for their potential life span and die simultaneously. Curve: S-curve
2.6.5 Succession: a series of events by which life comes back to an area, explains how ecosystems develop from bare substrate over a period of time. Primary succession: occurs on previously uncolonized substrate (e.g. rock) Pioneer species (e.g. lichens) colonize the area and make it more suitable for new species. Secondary succession: occurs where previous community has been destroyed (e.g. after forest fires), begins on existing soil. Faster than primary succession as a soil and seed bank is present.
Seral stages = sequence of different communities Sere = whole set of successive communities Climax communities feature: greater biomass high species diversity more K-strategists - tall, long-lived species steady-state equilibrium When succession is interrupted: climax community does not develop a stage of “plagioclimax” Human activities can interrupt succession, e.g. agriculture, hunting, burning
Zonation: Change in an ecosystem over distance/along a gradient. (spatial patterns of animals and plants). E.g. changes in ecosystems up a mountain with increasing altitude. Environment gradient: area where two ecosystems meet or where one ecosystem ends Methods to measure changes along a gradient: systematic sampling (transects), continuous transect, interrupted transect
The final stage in succession is called the climax stage and involves the climax community.